Chireix architecture using low impedance amplifiers

ABSTRACT

Circuits and methods for use in amplifying amplitude and phase modulated signals. A circuit uses a combiner with dual parallel signal amplifiers feeding it. The signal amplifiers have a low output impedance while the combiner does not provide any isolation between its inputs from the signal amplifiers. As in other Chireix architectures, the signals from the signal amplifiers are phase modulated prior to being fed to the combiner. The combiner then combines these two signals and, depending on how these two signals are combined, the resulting output of the combiner is amplitude modulated. The signal amplifiers may be Class D or Class F amplifiers to provide high efficiency amplification of the signals.

FIELD OF THE INVENTION

The present invention relates to signal processing and is particularlyapplicable but not limited to circuits for amplifying amplitude andphase modulated signals.

BACKGROUND TO THE INVENTION

The communications revolution of the 1990's has led to an increasingneed for further and better means of transporting both data and voicecommunications. One offshoot of this revolution has been the burgeoninggrowth in wireless communications as more and more data is beingtransmitted by wireless means. For wireless handsets, wireless PDAs(personal digital assistants), and other wireless devices, oneoverarching concern is power consumption—the less power a deviceconsumes the more desirable it is. To this end, higher efficiencycomponents, such as amplifiers, are desirable in these wireless devices.

One type of architecture which was used in the past but has fallen outof recent favor is the so called Chireix architecture. First suggestedby Henry Chireix in 1935, the technique also known as “outphasing”involves separately phase modulating two signals and recombining them ina combiner or combining network. By judiciously adjusting the phasemodulation of the two signals, the combined resulting signal can becomeamplitude modulated as well as phase modulated. This technique enablesthe use of saturated amplifiers or switching amplifiers for amplitudemodulated signals.

Also called “ampliphase” by the RCA Corporation when used in some oftheir radio transmitters, the technique has recently fallen out of favordue to its seeming inapplicability when amplifying signals. Previousattempts used common forms of linear and saturating amplifiers such asClass A and Class AB amplifiers to try and amplify the two signals priorto their being combined. Unfortunately, these efforts have yieldedunacceptable results as the resulting circuits were found to beinsufficiently efficient. A Chireix based architecture, if properlyworking with sufficient efficiency, would offer advantages in not onlypower consumption but in other areas as well.

Based on the above, there is a need for, methods or circuits whichovercome or at least mitigate the drawback of the prior art. Such asolution should provide the advantages of a Chireix or outphasingarchitecture while providing sufficient amplification efficiency to beuseful.

SUMMARY OF THE INVENTION

The present invention provides circuits and methods for use inamplifying amplitude and phase modulated signals. A circuit uses acombiner with dual parallel signal amplifiers feeding it. The signalamplifiers have a low output impedance while the combiner does notprovide any isolation between its inputs from the signal amplifiers. Asin other Chireix architectures, the signals from the signal amplifiersare phase modulated prior to being fed to the combiner. The combinerthen combines these two signals and, depending on how these two signalsare phase modulated, the resulting output of the combiner is amplitudemodulated as well as phase modulated. The signal amplifiers may be ClassD or Class F amplifiers to provide high efficiency amplification of thesignals.

In a first aspect, the present invention provides a circuit forproviding amplification to signals, the circuit comprising:

-   -   a signal combiner;    -   at least two signal amplifiers each receiving and amplifying a        signal, said signal amplifiers being coupled in parallel to said        combiner, each of said signal amplifiers acting as a voltage        source and having a low output impedance,        wherein    -   each signal received and amplified by each of said signal        amplifiers is phase modulated;    -   outputs of each of said signal amplifiers are added by said        combiner to produce a resulting signal; and    -   amplitude modulation and phase modulation of said resulting        signal from said combiner is achieved by an addition of said        outputs.

In a second aspect, the present invention provides a circuit forproviding amplification to signals, the circuit comprising:

-   -   at least two signal amplifiers each receiving and amplifying a        signal and each producing an amplifier output and acting as a        voltage source; and    -   an signal combiner receiving each of said amplifier outputs in        parallel, said signal combiner providing no isolation between        said amplifier outputs,        wherein    -   each signal received and amplified by each of said signal        amplifiers is phase modulated;    -   said amplifier outputs are added by said combiner to produce a        resulting signal; and    -   amplitude modulation of said resulting signal from said combiner        is achieved by an addition of said amplifier outputs.

BRIEF DESCRIPTION OF THE INVENTION

A better understanding of the invention will be obtained by consideringthe detailed description below, with reference to the following drawingsin which:

FIG. 1 is a block diagram of an amplifier system using a Chireixarchitecture according to one aspect of the invention;

FIG. 2 is a block diagram of a modified balanced magnetic transformerwhich may be used as a combiner in the system of FIG. 1;

FIG. 3 is a block diagram of a modified Wilkinson combiner which may beused as a combiner in the system of FIG. 1;

FIG. 4 is a block diagram of a Class-F power amplifier which may be usedas an amplifier in the system of FIG. 1; and

FIG. 5 is a block diagram of a Class-D power amplifier which may also beused as an amplifier in the system of FIG. 1.

DETAILED DESCRIPTION

Referring to FIG. 1, a block diagram of a circuit 10 according to oneaspect of the invention is illustrated. Signal amplifiers 20A, 20B feeda combiner 30 which produces an output 40. The signal amplifiers 20A,20B are low output impedance amplifiers while the combiner 30 is acombiner appropriate for Chireix architectures.

As in well known Chireix architectures, the signals received andamplified by the signal amplifiers 20a, 20B are phase modulated signals.These phase modulated signals, after being amplified by the signalamplifiers 20A, 20B, are combined or added by the combiner 30 to resultin the output signal 40. By judiciously phase modulating the signalsusing appropriate phase modulators (not shown), the resulting signal 40from the addition of the two signals is an amplitude modulated signal.Not only that, but the resulting signal is, in effect, an amplifiedversion of a phase and an amplitude modulated signal.

It should be noted that similar architectures as that illustrated inFIG. 1 have been attempted in the past. However, the low efficiency ofthe circuitry of the previous attempts stem from their use of lowefficiency amplifiers such as Class A and Class AB amplifiers which havesignificant output impedances. Such linear and saturating amplifiers didnot respond correctly to the dynamic adjustment of the load impedancebeing presented to them due to their significant output impedance.

The dynamic nature of the load impedance is a result of the appropriatecombiner for a Chireix architecture. Such an appropriate combiner notonly reinserts the amplitude modulation to the resulting signal 40, italso provides a dynamic adjustment of the load impedance presented toeach one of the signal amplifiers. This outphasing adjustment of theload impedance is such that the DC current through each signal amplifierdecreases as the combined output amplitude decreases thereby maintaininghigh efficiency.

Two appropriate combiners are illustrated in FIGS. 2 and 3. FIG. 2illustrates a modified balanced magnetic transformer. As is known in theart, magnetic transformer combiners normally have a center tap-to-groundconnection. In the modified transformer of FIG. 2, the tap-to-groundconnection is not present. As can be seen, each of the two terminals50A, 50B of an input winding 60 is to be coupled to a signal input or,in this case, a corresponding output of a corresponding signalamplifier. The output 70 is taken from one terminal of the outputwinding 80 while the other terminal 90 is coupled to ground 100.

Another appropriate combiner is a modified Wilkinson combiner 110 asillustrated in FIG. 3. As is known, a Wilkinson combiner has anisolating resistor which is normally coupled between the inputs. In themodified Wilkinson combiner of FIG. 3, neither of the inputs 120A, 120Bare coupled to the isolating resistor 130. This isolating resistor iseffectively not present in the modified combiner of FIG. 3. The resistor130 is provided merely for illustration. Other than this modificationrelating to the non-coupled resistor 130, the modified Wilkinsoncombiner 110 is similar in couplings and characteristics to other wellknown Wilkinson combiners.

Regarding a proper choice of amplifiers for use in the block diagram ofFIG. 1, it has been found by the inventors that either Class D or ClassF power amplifiers can correctly respond to the dynamic nature of theload impedance as mentioned above. These Class D or Class F poweramplifiers provide the desirably very low output impedances that allowsthe Chireix architecture to amplify both phase and amplitude modulatedsignals. Such a Class F power amplifier is illustrated in FIG. 4. ThisClass F amplifier 150 consists of a resistor load 160 coupled betweenground 170 and a capacitor 180. An inductor 190 also coupled in serieswith the capacitor 180 forms a resonator which passes the fundamentalharmonic of the signal to resistor load 160. Between the inductor 190and ground are coupled, in series, a high pass filler 200 and anotherresistor 210. The resistor 210 has a much higher resistance value thanthe load resistor 160. A shorted, quarter wave transmission line 220effectively shorts all even harmonic voltages while all odd harmonicvoltages, including the fundamental, are passed on. A switching voltageinput 230 is provided through a transistor 230.

As is known, Class F amplifiers provide a good approximation to avoltage square-wave across the output terminals of a device by“shorting” all even-harmonic voltages and “supporting” all odd-harmonicvoltages. As a result, the voltage waveform across the output terminalsof a device contains only odd-harmonic components. In addition, thissorting of odd- and even-harmonics results in a current passing throughthe output terminals of the device that contains the fundamental, andonly even-harmonic components.

This “shorting” and “supporting” of harmonics is conveniently achievedwith a shorted quarter-wave shunt-stub connected across the device'soutput terminals, a shown in FIG. 4. The stub will “short” the evenharmonics and “support” the odd harmonics. Since each harmonic willcontain only a voltage component or a current component, the device willnot absorb power, except at the fundamental.

In a practical situation, with a stub effectively shorting only thesecond harmonic voltage, and passing only the fundamental and thirdharmonic voltage, the power-added efficiency can be more than 85%.

As an example of a Class D amplifier which may be used with theinvention, FIG. 5 illustrates a block diagram of a Class D amplifier. Ascan be seen, the Class D amplifier is somewhat similar in structure tothe Class F amplifier of FIG. 4. Inductor 190, capacitor 180 andresistor load 160 form a series circuit. The inductor 190 is coupled inseries with one end of a transformer coil 240 while the other end of thetransformer coil 240 is coupled to ground 170. The other transformercoil 250 is tapped by a voltage source (Vcc) coupled to a groundedcapacitor 260. This other transformer coil 250 is coupled at each end toa switching voltage input 270A, 270B by way of transistors 280A, 280B.

For such Class D (voltage switching) amplifiers, the active devicepasses no current between its output terminals when the voltage acrossits output terminals is at the voltage rail, and passes maximum currentbetween its output terminals when the voltage across its outputterminals is zero. As a result, the device does not absorb any power,and all power taken from the bias supply is converted into the outputsignal (100% power-added efficiency).

It should be noted that the amplifiers in the amplifier pair 20A, 20B inFIG. 1 are to be of the same type. As such, if one amplifier 20A is aClass D amplifier, the other amplifier 20B should also be a Class Damplifier. Similarly, if one amplifier is a Class F amplifier, the othershould also be a Class F amplifier. These two amplifier classes providethe requisite switch mode operation along with the very low outputimpedance. Other amplifier classes may have the switch mode operationbut their output impedance is not of the desired very low value.

It should also be noted that while the circuit of FIG. 1 onlyillustrates two signal amplifiers in parallel, multiple signalamplifiers may be used in parallel with an appropriate combiner. Such aconfiguration may use multiple parallel signal amplifiers of the sametype or class, with all parallel signal amplifiers feeding a singlemultiple input port combiner. However, as noted above, these multiplesignal amplifiers are to have the requisite switch mode operation andthe low output impedance. Ideally, such a multiply parallel arrangementwould only use Class D or Class F power amplifiers.

A person understanding this invention may now conceive of alternativestructures and embodiments or variations of the above all of which areintended to fall within the scope of the invention as defined in theclaims that follow.

1. A circuit for providing amplification to signals, the circuitcomprising: a signal combiner, wherein said combiner is a modifiedbalanced magnetic transformer, said transformer being devoid of a centertap to ground connection; at least two signal amplifiers each receivingand amplifying a signal, said signal amplifiers being coupled inparallel to said combiner, each of said signal amplifiers having a lowoutput impedance and acting as a voltage source, wherein each signalreceived and amplified by each of said signal amplifiers is phasemodulated, and wherein at least one of the at least two amplifiers isconfigured to operate as a class F amplifier; outputs of each of saidsignal amplifiers are added by said combiner to produce a resultingsignal, said signal amplifier outputs being coupled to terminals of aninput winding of said transformer; and amplitude modulation of saidresulting signal from said combiner is achieved by an addition of saidoutputs.
 2. A circuit according to claim 1 wherein said combinerprovides minimum isolation between said outputs of said signalamplifiers.
 3. A circuit according to claim 1 wherein said combinerprovides no isolation between said outputs of said signal amplifiers. 4.A circuit according to claim 1 wherein each of said amplifiers hasswitch mode operation.
 5. A circuit according to claim 4 wherein each ofsaid amplifiers is chosen from a group comprising: class D signalamplifiers; and class F signal amplifiers.
 6. A circuit according toclaim 1 wherein all of said at least two signal amplifiers are of thesame type.
 7. A circuit for providing amplification to signals, thecircuit comprising: at least two signal amplifiers each receiving andamplifying a phase modulated signal and, each producing an amplifieroutput, and at least one of the at least two signal amplifiers operatingas a class F amplifier; and a signal combiner receiving each of saidamplifier outputs in parallel, said signal combiner providing noisolation between said amplifier outputs, wherein each signal receivedand amplified by each of said signal amplifiers is phase modulated; saidsignal combiner is a modified balanced magnetic transformer, saidtransformer being devoid of a center tan tap to ground connection; saidamplifier outputs are added by said combiner to produce a resultingsignals signal, said amplifier outputs being coupled to terminals of aninput winding of said transformer; and amplitude modulation of saidresulting signal from said combiner is achieved by an addition of saidamplifier outputs.
 8. A circuit according to claim 7 wherein each ofsaid signal amplifiers has a very low output impedance.
 9. A circuitaccording to claim 8 7 wherein each of said signal amplifiers has switchmode operation.
 10. A circuit according to claim 9 wherein each of saidsignal amplifiers is chosen from a group comprising: class D signalamplifiers; and class F signal amplifiers.
 11. A circuit according toclaims 7 wherein each of said signal amplifiers is chosen from a groupcomprising: class D signal amplifiers; and class F signal amplifiers.12. A circuit according to claim 7 wherein all of said at least twosignal amplifiers are of the same type.
 13. An apparatus, comprising: atleast two amplifiers each configured to amplify a corresponding phasemodulated signal; and a signal combiner configured to combine outputs ofsaid at least two amplifiers to produce a resulting signal; wherein saidcombiner includes a balanced magnetic transformer not requiring a centertap to ground; wherein the resulting signal is configured to beamplitude modulated via the corresponding phase modulated signalamplified by each of said at least two amplifiers; wherein at least oneof the at least two amplifiers is configured to operate as a class Famplifier; and wherein said outputs of said at least two amplifiers areconfigured to be coupled to terminals of an input winding of saidtransformer.
 14. The apparatus of claim 13, wherein said combiner isconfigured to provide minimum isolation between the outputs of said atleast two amplifiers.
 15. The apparatus of claim 13, wherein saidcombiner is configured to provide little or no isolation between theoutputs of said at least two amplifiers.
 16. The apparatus of claim 13,wherein one or more of said at least two amplifiers is configured tooperate in a switch mode.
 17. The apparatus of claim 13, wherein all ornearly all of said at least two amplifiers include a substantiallysimilar type of amplifier.
 18. An apparatus, comprising: at least twoamplifiers configured to amplify a corresponding phase modulated signal;and a signal combiner configured to combine outputs from said at leasttwo amplifiers to generate a resulting signal; wherein said signalcombiner is configured to provide little or no isolation between theoutputs of said at least two amplifiers; wherein said signal combinerincludes a balanced magnetic transformer not requiring a center tap toground connection; wherein the resulting signal is capable of beingamplitude modulated via the corresponding phase modulated signalamplified by each of said at least two amplifiers; wherein one of saidat least two amplifiers is configured to operate as a class F amplifier;and wherein said outputs of said at least two amplifiers are configuredto be coupled to terminals of an input winding of said transformer. 19.The apparatus of claim 18, wherein one or more of said at least twoamplifiers includes a low output impedance.
 20. The apparatus of claim18, wherein one of said at least two amplifiers includes a same orsimilar type of amplifier.
 21. An apparatus, comprising: means foramplifying two or more phase modulated signals; and means for combiningoutputs of said means for amplifying produce a resulting signal; whereinsaid means for combining includes a balanced magnetic transformer meansnot requiring a center tap to ground; and wherein the resulting signalis configured to be amplitude modulated responsive to the two or morephase modulated signals amplified by said means for amplifying; whereinsaid outputs of said means for amplifying are configured to be coupledto terminals of an input winding of said transformer means; and whereinthe means for amplifying includes at least one class F amplifier. 22.The apparatus of claim 21, wherein said means for combining isconfigured to provide a minimum isolation between the outputs of saidamplifying means.
 23. The apparatus of claim 21, wherein said means forcombining is configured to provide little or no isolation between theoutputs of said means for amplifying.
 24. The apparatus of claim 21,wherein said means for amplifying is configured to operate in a switchmode.
 25. An apparatus, comprising: means for amplifying two or morephase modulated signals; and means for combining outputs of said meansfor amplifying to generate a resulting signal; wherein said means forcombining is configured to provide little or no isolation between theoutputs of said means for amplifying; wherein said means for combiningincludes means for changing a voltage of a varying current and does notrequire a center tap means to ground connection; wherein the resultingsignal is configured to be amplitude modulated via the two or more phasemodulated signals amplified by said means for amplifying; wherein saidmeans for amplifying is configured to operate as at least one class Famplifier; and wherein said outputs of said means for amplifying areconfigured to be coupled to terminals of an input winding of said meansfor combining.
 26. The apparatus of claim 25, wherein said means foramplifying includes a low output impedance.
 27. A method, comprising:amplifying two or more phase modulated signals received at two or moreamplifiers; combining the two or more amplified signals with a balancedmagnetic transformer without requiring a center tap to ground to producea resulting signal; and amplitude modulating the resulting signalresponsive to the two or more phase modulated signals received at thetwo or more amplifiers; wherein outputs of said two or more amplifiersare configured to be coupled to terminals of an input winding of saidtransformer; and wherein at least one of the two or more amplifiers isconfigured to operate as a class F amplifier.
 28. The method of claim27, wherein said combining includes providing a minimum isolationbetween the two or more amplified signals.
 29. The method of claim 27,wherein said combining includes providing little or no isolation betweenthe two or more amplified signals.
 30. The method of claim 27, whereinsaid amplifying includes operating in a switch mode.
 31. A method,comprising: amplifying two or more phase modulated signals correspondingto two or more amplifiers; and combining the two or more amplifiedsignals with a balanced magnetic transformer without requiring a centertap to ground to produce a resulting signal; wherein said combiningincludes providing little or no isolation between the two or moresignals; wherein said amplifying includes operating the two or moreamplifiers in a switch mode; wherein said combining includes amplitudemodulating the resulting signal responsive to the two or more phasemodulated signals corresponding to the two or more amplifiers; whereinoutputs of said two or more amplifiers are configured to be coupled toterminals of an input winding of said transformer; and wherein at leastone of the two or more amplifiers is configured to operate as a class Famplifier.
 32. The method of claim 31, wherein said amplifying includesamplifying using two or more low output impedance amplifiers.
 33. Awireless device, comprising: a baseband processor; and a radio-frequencytransmitter coupled to said baseband processor, said radio-frequencytransmitter comprising; at least two amplifiers each configured toamplify a corresponding phase modulated signal; and a signal combinerconfigured to combine outputs of said at least two low output impedanceamplifiers to produce a resulting signal; wherein said combiner includesa balanced magnetic transformer not requiring a center tap to groundconnection; wherein the resulting signal is capable of being amplitudemodulated via the phase modulated signals corresponding to each of saidat least two amplifiers; wherein said outputs of said at least twoamplifiers are configured to be coupled to terminals of an input windingof said transformer; and wherein at least one of the at least twoamplifiers is configured to operate as a class F amplifier.
 34. Thewireless device of claim 33, wherein said combiner is configured toprovide a minimum isolation between the outputs of said at least twoamplifiers.
 35. The wireless device of claim 33, wherein said combineris configured to provide little or no isolation between the outputs ofsaid at least two amplifiers.
 36. The wireless device of claim 33,wherein one or more of said at least two amplifiers is configured tooperate in a switch mode.
 37. The wireless device of claim 33, whereinall or nearly all of said at least two amplifiers include a same orsimilar type of amplifier.
 38. A wireless device, comprising: a basebandprocessor; and a radio-frequency transmitter coupled to said basebandprocessor, comprising: at least two amplifiers configured to amplifycorresponding phase modulated signals; and a signal combiner configuredto combine outputs from said at least two amplifiers to generate aresulting signal; wherein said signal combiner includes a balancedmagnetic transformer not requiring a center tap to ground connection;wherein the resulting signal is configured to be amplitude modulatedresponsive to the phase modulated signal corresponding to each of saidat least two amplifiers; wherein said outputs of said at least twoamplifiers are configured to be coupled to terminals of an input windingof said transformer; and wherein at least one of the at least twoamplifiers is configured to operate as a class F amplifier.
 39. Thewireless device of claim 38, wherein one or more of said at least twoamplifiers includes a low output impedance.
 40. The wireless device ofclaim 38, wherein one or more of said at least two amplifiers includes asame or similar type of amplifier.